Abstract

The stimulation of time oxidative metabolism of frog muscle by insulin in vitro has been confirmed and its mechanism further explored in the sartorius muscle at 24°C. The oxygen consumption stimulation occurred even in the absence of added substrates and was proportional to the logarithm of the insulin concentration in the range of 0.05 to 50 mU/ml. The effect of insulin on oxygen consumption varied seasonally and was greatest in muscles from summer frogs in which the glycogen content was minimal. The addition of lactate alone also increased the consumption of oxygen, and time extra oxygen consumed in the presence of lactate was significantly increased by insulin. The increase was at least partly a result of a stimulation of the oxidation of the added lactate-1-C¹⁴ as determined by the recovery of C¹⁴O₂, but calculations indicate that insulin also stimulated the oxidation of endogenous substances. Insulin stimulated time incorporation of labeled lactate into muscle glycogen, but a net increase in the glycogen content of insulin-treated muscles was not found.